STFT's 'freeze' under decel (not decel fuel cut), lean tip in and rich tip out
Just noticed something on a car I'm tuning today that I've never seen before (99 SS camaro with a manual trans). The car seems to meet certain rpm or map conditions that tells it to freeze the fuel trims during decel. It doesn't flat line them like decel fuel cut, they just freeze with last value they had before coasting.
The car also goes very very rich under decel despite the ve table being reduced. The car is tuned SD, but would present the same issues with a MAF only tune as well. The fact that the fuel trims freeze sometimes makes this problem worse as extra fuel is being added on top of more than it should have.
The car has 36 lb Bosch (FAST) white injectors with a FAST 102 intake manifold. PRC 225 as-cast heads and a camshaft with 17 degrees of overlap. I'm pretty confident that the ve table is pretty good during steady state conditions, but the fuel swings pretty wildly with throttle transitions and I can 'feel' the lean bump when tipping into the throttle after a slow to normal shift.
I've installed these injectors in maybe 5 other f-bodies without any major issues and some of those cars had a 102 FAST as well. It seems like some kinda major transient issue but I wouldn't think that this setup should have transient issues. The injector data is all stock other than the injector flow rate....but these injectors are the same style as factory LS1 injectors and a 36 isn't a huge injector so I wouldn't think injector data would be the cause of this either.
Anyone ever seen this before? I've had other issues with this car so I almost wonder if there isn't an issue with the pcm or wiring. I've had a lot of trouble with the desired airflow at idle moving around drastically as if there were a vac leak even though all conditions were the same and no leaks can be found. Replacing the FAST tb with a NW seemed to help this problem a lot though.
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